The 18.0 migration of ``pos_payment_method_cashdro``
(`OCA/pos@6a4c251d <https://github.com/OCA/pos/commit/6a4c251d>`_) left three
uses of the 17.0 API that stop the CashDro integration from working. The module
has no tests nor tours and needs a physical drawer to be exercised, so nothing
in the OCA CI catches them.

This module patches the three of them from the outside, without touching the
OCA sources:

#. ``_cashdro_url()`` reads ``order.selected_paymentline``, replaced in 18.0 by
   ``order.get_selected_paymentline()``. Reading ``.payment_method`` on the
   resulting ``undefined`` raises a ``TypeError`` on every payment, which the
   caller swallows into a generic *"An error occurred while connecting to the
   cashdro"* message.
#. The ``add_paymentline`` patch checks ``line.payment_method``, renamed to
   ``line.payment_method_id`` in 18.0. The condition is never true, so the
   payment line keeps the default due amount instead of waiting for the amount
   the customer inserts in the drawer.
#. ``pos.session._loader_params_pos_payment_method`` is the 17.0 loading API,
   replaced in 18.0 by ``_load_pos_data_fields`` on each model. The override is
   dead code, so ``cashdro_host``, ``cashdro_user`` and ``cashdro_password``
   never reach the front end.
